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Extrapituitary TSH in early chick embryos: Pit-1 dependence?
1Department of Physiology, Perinatal Research Centre, University of Alberta, Edmonton, Canada.
Journal of Molecular Neuroscience : MN
|April 5, 2002
Summary
Thyrotropin (TSH) gene expression in chick embryos shows widespread TSH presence in extrapituitary tissues. Pituitary-specific transcription factor Pit-1 involvement in TSH expression is tissue-specific and not universal.
Area of Science:
- Developmental Biology
- Endocrinology
- Molecular Biology
Background:
- Pituitary-specific transcription factor Pit-1 is considered crucial for thyrotropin (TSH) gene expression in the pituitary gland.
- TSH immunoreactivity has been observed in various extrapituitary tissues, suggesting potential roles beyond the pituitary.
- The presence and function of Pit-1 in extrapituitary tissues during embryonic development remain largely unexplored.
Purpose of the Study:
- To investigate the distribution of Pit-1 and TSH immunoreactivity in embryonic chick tissues.
- To determine the potential involvement of Pit-1 in the extrapituitary expression of TSH prior to pituitary differentiation.
- To assess whether Pit-1's role in TSH expression is conserved across different embryonic tissues.
Main Methods:
- Immunohistochemical analysis was performed on embryonic chick tissues at the end of the first trimester (21-day incubation).
- Antibodies against TSH and Pit-1 were used to detect their respective immunoreactivities in various tissues, including brain, spinal cord, liver, lungs, gut, and limb buds.
- Co-localization studies were conducted to compare the distribution patterns of TSH and Pit-1.
Main Results:
- TSH immunoreactivity was detected in discrete cells across multiple extrapituitary tissues, including brain, spinal cord, liver, lungs, gut, and limb buds.
- Co-localization of TSH and Pit-1 immunoreactivity was observed in specific tissues like brain and spinal cord ependymal cells and liver hepatocytes, suggesting Pit-1-dependent TSH expression.
- However, several tissues exhibited intense TSH staining with minimal Pit-1 immunoreactivity (e.g., skin, limb bud, bronchus), indicating Pit-1-independent TSH gene expression.
Conclusions:
- Pit-1 is present in both pituitary and extrapituitary tissues of embryonic chickens.
- The involvement of Pit-1 in extrapituitary TSH expression in chick embryos is tissue-specific.
- These findings highlight a complex regulatory mechanism for TSH gene expression during embryonic development, with both Pit-1-dependent and Pit-1-independent pathways.